The present invention relates to an image producing device producing an image from which a reverse-side visible image included in input image data is removed.
As one of the problems of an image reading device, there is a problem of reverse-side visibility such that an image on a reverse side is seen through if the image also exists on the reverse side of an original document to be read, and also the image on the reverse side is captured when the image on the front side is read. The reverse-side visibility particularly occurs if the paper thickness of an original document is thin.
Some typical copying machines make the luminance of a background constant by skipping an image having luminance that is equal to or lower than a predetermined value, and remove an image itself visible on a reverse side in order to prevent such reverse-side visibility. However, if images having low luminance are uniformly skipped as described above, even an image on a front side, which is originally required although its luminance is low, may be skipped.
As a conventional device solving such a problem, for example, the technique disclosed by Japanese Laid-open Patent Publication No. 5-183749 exists. With this technique, the luminance distribution of background pixels is recognized to be a normal distribution, the luminance range of the background is obtained by using a most frequent value xe2x80x9cmxe2x80x9d of the luminance histogram as a standard, and the background (foundation) portion is separated from an image portion by defining an upper limit xe2x80x9c2mxe2x80x9d of the luminance range of the background as a threshold value.
Additionally, according to Japanese Laid-open Patent Publication No. 8-237485, a luminance histogram is taken, and background and image portions are separated by determining that the periphery of the most frequent value of the histogram to be a background, and by defining a luminance value which is slightly lower than that having the most frequent value to be a border.
Furthermore, according to Japanese Laid-open Patent Publication 10-257325, an image having luminance that is equal to or lower than that of a reverse-side visible section is not reproduced on recording paper by detecting a peak value from the luminance distribution of an image, by sectioning the luminance area into a background section, the visible section, and an image section based on the peak value, and by performing a binarization process with the use of the intermediate luminance between the image section and the reverse-side visible section as a threshold value.
Still further, according to Japanese Laid-open Patent Publication No. 11-41466, the luminance histogram of a captured image is generated, the luminance value Lp having the highest frequency and the maximum luminance value Lm are detected from the luminance histogram, whether or not reverse-side visibility exists is determined based on the difference between the obtained luminance value Lp having the highest frequency and the maximum luminance value Lm, and the background luminance Ls of an original document is decided based on the luminance value Lp having the highest frequency if the reverse-side visibility is determined not to exist, or the background luminance Ls of the original document is decided based on the maximum luminance value Lm if the reverse-side visibility is determined to exist.
Still further, according to Japanese Laid-open Patent Publication No. 1-213073, a color image is captured, histograms are generated for the respective primary colors xe2x80x9cRxe2x80x9d, xe2x80x9cGxe2x80x9d, and xe2x80x9cBxe2x80x9d, and a conversion table is generated by defining a certain density from a peak occurring in a portion the color density of which is close to white to be a threshold value xe2x80x9cCxe2x80x9d, and a white density is evenly output to colors the densities of which are whiter than the threshold value xe2x80x9cCxe2x80x9d, so that the background color is made uniform.
Still further, according to Japanese Laid-open Patent Publication No. 1-196975, pre-scanning is performed when a color image is read, and histograms for the respective RGB of the read image are generated, a threshold value for removing a background color is set, a color brighter than the threshold value is converted into the most brightest color (white) as a background color, so that the background color is removed.
However, the image reading devices recited in the above described publications have the following problems.
Japanese Laid-open Patent Publication Nos. 5-183749 and 8-237485 assume that the portion in which the luminance of image data or the luminance value having the highest frequency exists is a background. Therefore, for example, if there are many reverse-side visible portions, and if the most frequent value is configured by the luminance of a reverse-side visible portion or a luminance value, background luminance or luminance is improperly detected. This is because the most frequent value itself does not represent the background luminance or the luminance.
Since the presence/absence of a reverse-side visible portion is determined by using the association between the peak luminance Lp and the maximum luminance Lm of an original text such as general book information according to Japanese Laid-open Patent Publication No. 11-14166, the presence/absence of a reverse-side visible portion is improperly detected, or the background luminance Ls of the original is improperly decided if a background color is applied to the whole of the original, such as a color magazine, etc.
Japanese Laid-open Patent Publication No. 10-257325 assumes the boundary between a reverse-side visible portion and an image portion from the peak position of density values of a multi-valued image by targeting a monochrome image, and removes the reverse-side visibility with binarization. Accordingly, this technique cannot be applied to a color image or the case where a multi-valued image is required after a reverse-side visible portion is removed.
According to Japanese Laid-open Patent Publication No. 1-213073, a color image is targeted, and a background color is uniformly converted into a bright color. Therefore, if the original background color is dark in the case where a dark reverse-side visible portion exists in the entire image, the background color may be converted into a bright color.
Because Japanese Laid-open Patent Publication No. 1-196975 aims at reducing an amount of toner, a background color is not reproduced. Accordingly, even if a particular background color exists in a reverse-side visible portion, the background color is entirely converted into pure white.
If reverse-side visibility occurs, a text image on the reverse side overlaps the text portion of the image on the front side, and appears on the front side, leading to a big obstacle to viewing of a text image included in an image.
Accordingly, if an original image is read by image reading means and stored onto a magnetic storage medium, etc., it is desirable to record only the front side of the original document read by the image reading means.
An object of the present invention is to provide an image producing device removing a reverse-side visible image from a background color without damaging the hues of an image so much even if a color is applied to the background of an original.
An image production controlling device according to one aspect of the present invention, which outputs input image data by removing a reverse-side visible portion of the image data, comprises a histogram generating unit generating a luminance value histogram for at least one color from image data, a most frequent value deciding unit deciding the luminance value having the highest frequency from the histogram, and a background candidate luminance area deciding unit deciding an area having a luminance value which will become a background candidate in the neighborhood of the most frequent value.
An image producing device according to another aspect of the present invention, which outputs input image data by removing a reverse-side visible portion from the image data, comprises an image data obtaining unit obtaining image data, a first storing unit storing the obtained image data, a histogram generating unit generating a luminance value histogram for at least one color from the image data stored in the first storing unit, a most frequent value deciding unit deciding the luminance value with the highest frequency, and a background candidate luminance area deciding unit deciding an area having a luminance value which will become a background candidate in the neighborhood of the most frequent value.
An image production controlling method according to one aspect of the present invention, with which input image data is output by removing a reverse-side visible portion from the image data, comprises: generating a luminance value histogram for at least one color from image data; determining the luminance value having the highest frequency from the histogram; and deciding an area having a luminance value which will become a background candidate in the neighborhood of the most frequent value.
The method according to the present invention further comprises: deciding a luminance value to be defined as background luminance within the area; and replacing the luminance value of the image data within the area with the luminance value to be defined as the background luminance. This method is installed on an image production controlling device or an image producing device.
As described above, according to the present invention, a histogram is generated from image data, and the most frequent value of the histogram is obtained. The luminance value corresponding to the most frequent value indicates the luminance value of a reverse-side visible portion. Therefore, the area of the image, which has the luminance value in the neighborhood of the most frequent value within the histogram, is defined to be a reverse-side visibility area, whereby the area in which the reverse-side visibility occurs within the image can accurately be identified and an effective means for removing a reverse-side visible portion is provided.
Additionally, a reverse-side visible portion can be removed without damaging the hues of a background by obtaining the luminance value to be defined as background luminance, and by replacing the obtained value with the luminance value of the area.